Semaphore Identity example code bug fix (Fix #848) (#849)

* Semaphore identity example code bug fix

* Receive suggestion for consistency

---------

Co-authored-by: weipooppys93030 <55434365+weipooppys93030@users.noreply.github.com>

Author: csiejimmyliu

packages/identity/README.md

@@ -125,7 +125,7 @@ import { Identity } from "@semaphore-protocol/identity"
 const message = "message"
 const identity = new Identity()
 
-const signature = identity.signMessage("message", signature)
+const signature = identity.signMessage(message)
 
 Identity.verifySignature(message, signature, identity.publicKey)
 ```